Covering the World of Communication Sciences and Disorders

Audiology in Brief: November 20, 2012

Disappearing Sounds Harder to Detect

Brains are better at hearing new and approaching sounds than at detecting when a sound disappears, a phenomenon researchers call "disappearance blindness." The findings could aid the design of devices intended to help professionals such as air traffic controllers and pilots, who operate in environments in which the detection of changing sounds is critical.

Hearing acts as an early warning system to direct our attention to new events. But researchers at the University College London Ear Institute wanted to understand what makes some sounds easily detectable while others go unnoticed. They created artificial "soundscapes" composed of different ongoing sounds—such as voices, barking dogs, and environmental noises—and asked approximately 84 male and female listeners to detect the onset or disappearance of different sound-objects.

Overall, the team found that listeners are tuned to detecting new sounds around them but are much less able to detect when a sound disappears. In busy sound environments, participants missed more than half of the changes occurring around them, and the changes that were detected involved much longer reaction times. The effects were observed even in the presence of only a few different sounds, and didn't seem to be affected by volume. Search doi: 10.1371/journal.pone.0046167.

Impaired Ears Hear Differently in Noise

Background noise causes the ears of people with hearing impairment to work differently, Purdue University researchers have found. The findings, published in Nature Neuroscience, could influence the design of hearing aids and assistive technologies.

Researchers measured a variety of physiological markers in chinchillas—some with normal hearing and others with a cochlear hearing loss—as they listened to tones in quiet and noisy environments. Chinchillas were used because their hearing range is similar to that of humans, and background noise was used in the study to simulate what people would hear in a crowded room.

The researchers focused on coding of the temporal fine structure of sound, which is critical to perception of speech in everyday listening environments. The auditory system filters sound into channels tuned to different frequencies, and those channels vary based on their frequency tuning. In a normal system, the channels are sharp and focused, but the study's results suggest they get broader and more scattered with hearing impairment.

The results suggest that hearing aid designers' primary focus should be on improving noise-reduction algorithms so devices provide a clean signal to the auditory nerve. Next, the researchers plan to expand the study to focus on more real-world noises. Search doi: 10.1038/nn.3216.

Netflix to Provide Closed Captions

Netflix, Inc., and the National Association of the Deaf (NAD) have reached an agreement that 100% of Netflix's online, streaming content will be closed-captioned by 2014. The disability civil rights lawsuit was brought against Netflix in 2010 by Lee Nettles, a Massachusetts resident who is deaf, and the NAD. The lawsuit, National Association of the Deaf v. Netflix, is remarkable in that a federal judge's ruling established that web-only firms are subject to the Americans With Disabilities Act. Netflix currently offers closed captioning for approximately 90% of its streaming content, and has committed to increase the visibility of captioned content until all of it is accessible. Visit the NAD website for more information.